This invention relates in general to color television picture tubes and in particular to a method for assembling the glass funnel and faceplate parts of such tubes. Conventionally, a color television picture tube has a glass bulb including a funnel and a flanged faceplate sealed to the flared end of the funnel. An electron gun assembly mounted in a neck portion of the funnel provides a source of electrons which impinge on an electron-excitable phosphor screen deposited on the concave inner surface of the faceplate.
A well-known technique for assembling the parts of a glass bulb employs a frit-type of glass sealing material. The frit is usually applied to a seal land on the flared portion of the funnel with the funnel supported in a neck-down position. A seal land on the faceplate is then superposed thereover with the two seal lands in registration with one another. The envelope assembly is then heat treated in an oven having an appropriate heat profile and time cycle to permit the frit to establish a vacuum-type seal all along the sealing interface of the faceplate and funnel.
This entire process is well understood and is successfully practiced in the production of shadow mask color picture tubes of a conventional type on a mass production basis. Great care is exercised in the fabrication of the component parts and in the various processing steps to assure proper and precise beam landing in the finished tube. For example, the seal lands of the faceplate and funnel are frequently precision ground in an effort to attain an optimum mating of these sections in the sealing process.
The method of this invention is believed to be most useful when applied to a tube having a flangeless faceplate. Such a tube is disclosed in U.S. Pat. No. 3,894,260 issued to the assignee of this application. The tube has a flangeless, curved glass faceplate, a concave inner surface of which receives a phosphor screen. The funnel portion of this unique tube has a convex, curved seal land; that is, the seal land defines a convex, curved plane which matches and mates with the curvature of the concave inner surface of the faceplate. Since the faceplate is flangeless, the sealing interface between the funnel and the faceplate is curved rather than planar as in conventional tubes.
In order to insure proper beam landings in this unique tube, an internal referencing system is provided for accurate positioning of the faceplate relative to the funnel in an assembled tube. An internal referencing system for use with this unique tube is disclosed in copending application Ser. No. 462,915 filed Apr. 22, 1974 now U.S. Pat. No. 3,971,490 and U.S. Pat. No. 3,904,914, both assigned to the assignee of this application.
Copending application Ser. No. 462,915, filed Apr. 22, 1974 discloses a unique rectangular-type color cathode ray tube in which the faceplate and the tube funnel have referencing means which define faceplate and funnel reference surfaces of such number and arrangement that the faceplate and the funnel are interlocked to prevent beyond-tolerance relative movement therebetween. In a preferred structure disclosed, the faceplate has internal referencing means in three corners. The funnel has in each of three corresponding corners an integral notch defining a pair of spaced, inside funnel reference surfaces oriented to capture the associated faceplate referencing means.
U.S. Pat. No. 3,904,914 discloses a unique rectangular-type color cathode ray tube which has an envelope, comprising an approximately rectangular, flangeless faceplate having in at least three perimetric interior regions thereof referencing means, the referencing means defining at least three faceplate reference surfaces. A funnel having an approximately rectangular mouth is sealed to the faceplate. The funnel is provided with a like number of inside funnel reference surfaces in alignment with the faceplate reference surfaces for making referencing engagement with the faceplate reference surfaces when the faceplate and funnel are assembled. The faceplate and funnel reference surfaces are of such number and arrangement as to uniquely determine and fix the location of said faceplate relative to said funnel. In a preferred embodiment, the referencing means on the faceplate comprise corner-mounted studs serving also to hold a color selection electrode for the tube.
A number of problems have been encountered in attempting to assemble a tube having a flangeless faceplate of the type described above. For example, when the faceplate is placed on the funnel by hand, it is difficult to see if the faceplate and funnel are properly aligned before lowering the faceplate onto the funnel. If not aligned, it is possible to damage the frit material located on the funnel seal land, thereby causing problems in the operation of the tube when it is fully assembled and evacuated. A high degree of precision is required to properly assemble a flangeless faceplate and a funnel of the type of tube described above. The method of this invention solves the problem of assembly for this type of tube.